Pressure reducing regulators consisting of controllable valve arrangements capable of providing a constant outlet pressure over a wide range of variable source pressures are well known and available commercially. A controllable diaphragm arrangement, or a piston device, in communication with the outlet pressure generally is used to adjust the valve opening in response to outlet pressure variations. The diaphragm operates in response to two forces, one, a controllable reference force produced by biasing means such as a range spring having adjustable compression or by an adjustable quantity of trapped gas or a combination thereof, and two, the force on the diaphram surface from the outlet pressure of the fluid downstream from the valve arrangement. The diaphragm operates to adjust the valve opening such that these two forces are equal and stable. If fluid is rapidly withdrawn from the outlet side of the valve arrangement, the outlet pressure will drop, and the range spring force will shift the diaphragm to open the valve further and maintain constant outlet pressure. If the outlet pressure increases, e.g., because the regulator valve opens too far or because fluid flow from the downstream side of the valve arrangement ceases or diminishes, the force of the outlet pressure on the diaphragm will shift the valve toward a closed position and prevent upstream source pressure from increasing the outlet pressure above that constant level which balances the assigned reference force.
However, in the event of fire or intense heat within the regulator or other system component such as a relief valve or downstream tubing, the diaphragm is frequently breached, with the resultant undesirable effect of an elimination of the outlet pressure force on the diaphragm and an escape of the flowing gas past the diaphragm through the spring cage and breaking the integrity of the housing. The range spring force then shifts the valve to an open position, thereby supplying a greatly increased flow of fluid to the fire. Such a condition becomes extremely critical when the controlled fluid is an oxidant, in which case increased fluid flow accelerates the fire.
Paine, U.S. Pat. No. 1,140,313, shows an automatic safety device having a fusible element external to the valve arrangement for cutting off the flow of combustible fluids. A diaphragm takes the place of packing to prevent leakage around the valve stem.
Lovekin, U.S. Pat. No. 1,248,143, discloses a valve arrangement wherein a first fluid, such as a fuel stream to a domestic hot water heater, is closed by a valve upon the melting of a fusible element in a second fluid line, such as the hot water pipe. A diaphragm is used in the hot water pipe to provide a leakage prevention device which is extendable with the valve stem.
McKhann, U.S. Pat. No. 3,608,570, shows yet another valve system, which like the aforementioned patents is incapable of acting as a pressure regulator, in which the valve is moved to a closed position by an external fusible material in response to a high temperature condition.
Guimbellot, U.S. Pat. No. 3,730,205, shows a simple valve system, not a pressure regulator, having a fusible plug which softens at elevated temperatures or upon prolonged contact with crude oil. The softened plug is capable of closing an otherwise constantly open valve.
Collins, Jr. et al, U.S. Pat. No. 3,911,948, which patent is owned by the assignee of the present invention, shows a pressure regulator for delivering an oxidant gas from a high pressure source to a lower adjustably controllable and constant pressure. Critical problems associated with oxidant fluids in a pressure regulator are minimized by substituting proper materials of construction for combustible materials normally used for valve seating.
In many cases, the heat and temperature of the fluid inside a piping system may be higher or more critical than the external temperature of the surrounding area, e.g., with steam in high temperature, high pressure pipes or with oxidant fluids such as in oxygen delivery. In the event of fire or extremely hazardous high temperatures interior to a pressure regulator having a diaphragm controlling mechanism to provide a constant outlet pressure, the diaphragm is frequently breached, whereupon the regulator fails in the open position. For these and other applications, a pressure regulator for delivering a constant outlet pressure and having an automatic safety shutoff responsive to internal high temperatures or fire would be highly desirable for safety reasons.